6.2 sum: Print checksum and block counts

sum computes a 16-bit checksum for each given file, or
standard input if none are given or for a file of ‘-’. Synopsis:

sum [option]… [file]…

sum prints the checksum for each file followed by the
number of blocks in the file (rounded up). If more than one file
is given, file names are also printed (by default). (With the
--sysv option, corresponding file names are printed when there is
at least one file argument.)

By default, GNU sum computes checksums using an algorithm
compatible with BSD sum and prints file sizes in units of
1024-byte blocks.